Weather proofing electronics without potting (for prototypes)?

[e100]

Has anyone had success using the newer "modified silicone" type caulk type sealants available from hardware stores to weatherproof electronics and cable entries without going to the extreme of potting the whole thing?

Currently I'm using a solvent based synthetic rubber caulk that sticks to almost everything but the toluene solvent is incompatible with many plastics and it takes days or weeks for it to fully cure.   

Conventional silicones for glazing and roofing repairs don't adhere to PVC cable jackets whereas the modified silicones do adhere (to some degree). I know that the brands vary from by country, in Australia we have "Selleys wet area" modified silicone which cures to a soft rubber like consistency. It's not as strong as normal silicone rubber and has a lower tear strength, but it has better adhesion. I have a half used tube of the stuff which is still usable a year after it was first opened, so the long shelf life is definitely a bonus when only small quantities are being used at infrequent intervals. I have no idea how compatible it is with electronic circuits etc.


Mike

[ramonest]

For cable entries wouldn't the best option be an O ring (not sure how it's written only heard it on youtube videos) tightened with a bolt? I don't know if it has a technical name but I've seen and used it for example for the cable entry hole on a pump control system, the pump itself, etc... I'm not sure if it's water proof ut it sure is weather and moisture proof.
Using adhesives like silicone might be annoying if you have to repair it or plan to change it. If you are sure that that must last long, can't pit O ring, I've used some type of cement that when dried looks like glass and for now it keeps the roof without leaks. I don't remember the name but we bought it on a construction material place.
Hope someone can help you better tough!

[SeanB]

I would rather use either a wax or a petroleum gel to do a weatherproof prototype, as the wax or gel repels water, yet is easy to remove ( at least easier than silicone) for modifications or rework.  For cable entry use a cable gland with integrated seal, the common electrical gland ( not those used in the USA, the proper ones with a rubber sealing ring that grips the cable sheath) works pretty well here, especially is you just use a bit of extra sealer on the threaded entry into the box and a blob on the outside to cover it all up.

I have made waterproof junctions in ponds using only a standard junction box with 2 glands, and sealing the cables in it with PVC weld and putting the top on after a Vaseline coat on the connections, and sealing with PVC tape and more PVC weld on the lid to hide the screws. Hauled the pump out after 3 years when it failed, smashed the box open and reused the one gland on the next box ( it came off intact with the cable still welded in it) to connect the pump. Inside the copper was still shiny, and was dry.

[bicc1306]

I would use weather proof cable glands.

[Trigger]

Boeshield T6 leaves a coating that will weatherproof electronics.  Corrosion X will do the same but T6 will dry to a waxy type coating while Corrosion X is a bit like an oil coating instead.  With T6 make your connections before coating the board or you'll be cleaning contacts before anything will work.

[Ian.M]

Sillicone sealants generally suck except on extremely carefully cleaned and prepared surfaces.   As they cure they tend to leave a film of byproducts of their polymerisation on any surface that they have failed to chemically bond to, which then hydrolyses, corrodes vulnerable surfaces and provides a path for capillary wicking that can actually worsen the moisture ingress problem by encouraging it to flow uphill! 

If you need an adhesive sealant, look at low VOC polyurethane mastics - they generally have excellent adhesion to metals and most plastics, but you do need to check the manufacturer's plastics compatibility tables.

Finally, it is absolutely critical to have some means of equalising interior and exterior pressure to avoid your enclosure sucking in moisture as the air inside cools every dewy night and anytime its rained on after being in direct sunshine.  A drain hole in the bottom of the enclosure may be suitable, otherwise you need to look at using a Goretex vent or pressure equalising bladder or running a vent tube to a dry location.

[KL27x]

Conventional silicones for glazing and roofing repairs don't adhere to PVC cable jackets

For this, I would spread a layer of the silicone to extend it over a short section of the PVC cable jacket. Then wrap one layer of twine, tightly, over this section, squeezing out the silicone to the top of the twine. Then spread the silicone over the twine to ensure it is waterproof. This composite fiber construction will keep the silicone from separating from the flexible PVC.

Silicone will maintain a watertight seal, as long as it is not allowed to "tear away" from the other material. It doesn't "stick" to plexiglass, for instance. But I have a leakproof plexiglass tank sealed with silicone, using nylon bolts to maintain positive pressure.

I do the twine trick mostly with hot glue, to be clear. I don't use a lot of silicone. But it works great with hot glue, where I have used it for exactly this kind of application. I think of it Giligan's Island carbon fiber. Even with solvents and a knife, it is VERY difficult to remove. Due to the cumulative compression of the cord wrap and the perfect molecular fit of the hot glue to the sheath, and the excellent adhesion of the glue to the twine, there is practically no way to silp the pvc out of the hot glue sheath with brute force, even with alcohol added. It's one piece. The PVC cable sheath is basically not allowed to stretch/flex anymore than the twine/glue allow it to. To remove, each strand of string has to be cut and alcohol applied. I would guess it would work the same with silicone but can't be 100% sure.